In recent years, photoelectric elements have been used as, for example, electricity generation elements (e.g., a photovoltaic cell and a solar cell), which generate electricity by means of photoelectric conversion, light-emitting elements (e.g., an organic EL element), optical display elements (e.g., an electrochromic display element and an electronic paper), and sensor elements sensing temperature, light, or the like. Among them, a p-n junction element has been put into practice as a photoelectric element for a solar cell or the like. In addition, various photoelectric elements using techniques with regard to photoelectrochemistry have been developed as disclosed in Patent Literature 1. This photoelectric element is prepared by interposing a charge-transport layer containing an electrolyte or the like between a first electrode with a semiconductor attached and a second electrode. The semiconductor typically supports a dye, which is a photosensitizer, and therefore the photoelectric element is used as a dye-sensitized solar cell. Accordingly, applying light to the semiconductor makes the semiconductor to generate charges; the charges transfer through the charge-transport layer; and electricity can be extracted to the outside through the first electrode with the semiconductor as the negative electrode (anode) and through the second electrode as the positive electrode (cathode).
With regard to a photoelectrochemical device including such a photoelectric element, Patent Literature 2 discloses that a radical compound is provided so as to be in contact with a semiconductor. In this device, careers (holes or electrons) generated through irradiation of the semiconductor are involved in a redox reaction (oxidation-reduction reaction) of the radical compound, and the radical compounds serve as a redox pair, which causes an electrochemical oxidation or reduction. Therefore, speed of a response to irradiation of the semiconductor is increased, and stability and reproducibility are improved.
However, in the device as shown in Patent Literature 2, with regard to electrons and holes which are separated by photosensitizer, a transfer of charges is not performed efficiently in a process that holes transfer to an electrode, and therefore photoelectric conversion efficiency is insufficient.